Most structural components include stress concentrations at notches, fillets, slots, radii cutouts and holes in the component material. The fatigue and crack growth life of holes can be significantly improved by cold-expanding the material immediately bounding the holes. Typical tooling and techniques for cold-expanding circular openings are disclosed, for example, in U.S. Pat. No. 4,557,033, granted Dec. 10, 1985, to Robert L. Champoux. Life-enhancement techniques for noncircular stress concentrations have been traditionally limited to surface treatments such as shot peening, roller burnishing, coining, etc. These methods create relatively shallow zones of residual compressive stresses, are often sensible to manufacturing variables, and are dependent on the proficiency of the operator. The cold-expansion process, involving the pulling of a cold-expansion mandrel through a circular opening, either alone or through a cold-expansion sleeve positioned in the opening, is known to be a reliable and effective method of material life enhancement. It is insensitive to manufacturing variables. Also it is independent of operator proficiency.
The principal object of this invention is to use a mandrel only cold-expansion technique, or a mandrel and sleeve cold-expansion technique, for life enhancement of dovetail connector slots.